This application is based upon Japanese Patent Application Nos. Hei. 10-313982 filed on Nov. 9, 1998, Hei. 11-212731 filed on Jul. 27, 1999 and Hei. 11-264335 filed on Sep. 17, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to an electric apparatus, and particularly to an electric apparatus in which an electric signal from a heat-emitting element is output through an electrode member by contacting the heat-emitting element with the electrode member, and further particularly to an electric apparatus which can reduce an electric resistance and a thermal resistance between the heat-emitting element and the electrode member, and to a method of manufacturing the same.
2. Related Art
There has proposed a pressed-contact semiconductor device in which a main electrode surface of a semiconductor element (heat-emitting element) contacts with an electrode plate (electrode member) together by being externally pressed (hereinafter, this contact is called xe2x80x9cpressed-contactxe2x80x9d). Such the device is known as a structure in which a first main surface of the semiconductor element such as a thyristor as a large passing current power transistor, an IGBT (Integrated Gate Bipolar Transistor) and a large capacitor diode, is bonded by brazing, soldering or the like and a second main surface of the same is contacted with an electrode plate by the pressed-contact, or a structure in which the first main surface and the second main surface are sandwiched by electrode plates.
Recently, this kind of semiconductor element has been developed to be more and more large capacity in order to increase a rated current. Therefore, it becomes necessary to reduce a contact electric resistance and a contact thermal resistance between the semiconductor element and the electrode plate, and between the electrode plate and an insulating plate or a radiating plate (heat sink) to improve a use-efficiency and a durability of the semiconductor element.
In order to comply such a request, several semiconductor devices shown in Japanese Patent Application Laid-open No. 54-40569 and No. 54-95183 have proposed. In the former applications, an intermediary member made of oil or grease in which powder metal is mixed therein is intercalated between a main electrode surface of the semiconductor element and the electrode plate, and being held by being pressed to reduce the electric and thermal contact resistances. However, since the oil or grease including the powder metal is an insulator as itself, it is difficult to sufficiently reduce the electrical resistance. Furthermore, since these chemical synthetic materials have poor thermal conductivities compared to metal, it cannot say that this structure can sufficiently reduce the thermal resistance.
On the contrary, in the latter application, an intermediary member made of powder metal layer whose particle diameter is to or less than 2 xcexcm is intercalated between the main electrode surface of the semiconductor element and the electrode plate, and being held by being pressed to reduce the electric and thermal contact resistances. However, in this case, the number of interfaces defined among each particles whose particle diameter is to or less than 2 xcexcm becomes remarkably large. Therefore, although each resistance (especially electric resistance) at each interface is small, the resistance as the whole of the powder metallic layer becomes large compared to that of a bulk metal having an equal thickness. Hence, it also cannot say that this structure can sufficiently reduce the electric resistance between the main electrode surface of the semiconductor element and the electrode plate.
Furthermore, another countermeasure has proposed in Japanese Patent Application Laid-open No. 8-330338. In this application, a contact intermediary member made of soft metal foil is intercalated between the main electrode surface of the semiconductor element and the electrode plate to improve an electric contact therebetween. However, since a surface roughness of the soft metal foil is so small like a mirror surface, the contact intermediary member cannot fill up a small gap caused by an asperity of the main electrode surface of the semiconductor element or the surface of the electrode plate. Therefore, it is difficult to sufficiently reduce, especially, the thermal resistance.
Such an inconvenience described the above is thought to be common among electric apparatuses (hereinafter, called xe2x80x9celement-electrode contact type electric apparatusxe2x80x9d) in which an electric signal from a heat-emitting element is output through an electrode member by contacting the heat-emitting element with the electrode member.
Incidentally, in the element-electrode contact type electric apparatus, a thermal buffer plate is intercalated between the heat-emitting element and the electrode member in order to reduce physical damages to the heat-emitting element. Here, physical damages include such as a load concentration due to a thermal distortion between the heat-emitting element and the electrode member during making the pressed-contact, or a wear of a contact surface (especially, the surface of the heat-emitting element) due to a difference in thermal expansion. However, the electric resistance and the thermal resistance between the heat-emitting element and the electrode member become large due to the thermal buffer member intercalating therebetween.
In order to solve this inconvenience, a countermeasure, in which the electrode member has a thermal buffer function so as to reduce the number of the component parts, has proposed in Japanese Patent Application Laid-open No. 1-228138. According to this application, a metallic plate, which contacts with both an anode and a cathode of a semiconductor element, is made of molybdenum (Mo) plate whose thermal expansion coefficient is close to that of silicon (Si), which is a main material of the semiconductor element. And then, the Mo plate is also used as an electrode contacting with an external conductor so that the number of the component parts reduces.
Although such a structure needs to provide a radiating plate (heat sink) via an insulating plate at outer side of the electrode member (thermal buffer electrode member) to radiate heat externally, this application does not disclose any methods to independently take out electric current and heat emitted by the semiconductor element.
On the contrary, a insulating plate for separating a radiating path and a current path by being intercalated between the electrode member and the radiating plate is disclosed in Japanese Patent Application Laid-open No. 62-287649. In this application, a bulk ceramic is intercalated between the heat sink and the electrode terminal for outputting signal from the semiconductor element to isolate each other, and a soft metal foil is further intercalated between the ceramic plate and the heat sink so that a radiating efficiency is improved.
Therefore, it may be thought to employ the bulk ceramic as the insulating plate to be intercalated between the thermal buffer electrode member and the radiating plate. However, the thermal resistances at an interface between the electrode member and the ceramic plate and an interface between the radiating plate and the ceramic plate are not negligibly small. Furthermore, the thickness of the-ceramic plate needs to have enough thickness for assembling and handling.
Therefore, it also cannot say that this structure can sufficiently reduce the thermal resistance. Hence, according to the conventional structure as described the above, it is difficult to sufficiently reduce both the electric resistance and the thermal resistance between the heat-emitting element and the electrode member, even when the thermal buffer electrode member is used as the electrode member to reduce the number of the component parts.
This invention has been conceived in view of the background thus far described and its first object is to reduce both an electric resistance and a thermal resistance between a heat-emitting element and an electrode member, which are contacted with each other.
Its second object is to reduce both an electric resistance and a thermal resistance between a heat-emitting element and an electrode member in an electric apparatus in which the heat-emitting element is sandwiched by a pair of electrode members as thermal buffer electrode member, and the electrode members are further sandwiched by a pair of radiating members.
According to the present invention, a contact intermediary member is made up with first members having a first average diameter and having an electric conductivity and a thermal conductivity, and second members having a second average diameter smaller than the first average diameter and having an electric conductivity and a thermal conductivity. In this invention, the number of interface between each large member is reduced so that an electric resistance is reduced by the first members, and total contact area is increased so that the thermal resistance is reduced by the second members having the second average diameter. Therefore, it can provide a pressed-contact type semiconductor device in which a main electrode surface of a semiconductor element is contacted with an electrode plate by a pressed-contact, which can reduce both an electric resistance and a thermal resistance between the main electrode surface of the semiconductor element and the electrode plate.
According to another aspect of the present invention, a contact intermediary member is made up with a metal foil having surfaces contacted with the heat-emitting element and the electrode member, the surfaces being deformed to increase contact areas between the heat-emitting element and the electrode member; and powder metal intercalated into gaps formed between the deformed surfaces and both the heat-emitting element and the electrode member. In this invention, electric resistance is reduced by the metal foil, and total contact area is increased so that the thermal resistance is reduced by the powder metal having. Therefore, it can provide a pressed-contact type semiconductor device in which a main electrode surface of a semiconductor element is contacted with an electrode plate by a pressed-contact, which can reduce both an electric resistance and a thermal resistance between the main electrode surface of the semiconductor element and the electrode plate.